SE534876C2 - Method of providing a substrate with a barrier using electrospinning or melt spinning of nanofiber - Google Patents

Abstract

The invention relates to a method for providing a surface of a fiber-based substrate with a barrier layer, the barrier layer being formed by applying nanofibers to the surface by using electrospinning or melt spinning. The invention also relates to a substrate containing such a barrier layer.

Description

534 875 paper or board at the same time as it is possible to disintegrate the barrier coated paper or board which facilitates recycling of the fiber-based substrate used.

Forming a barrier layer by using dispersion coating can make it difficult to obtain all the necessary properties for the package or product thereof. The heat sealability and good barrier properties are typically difficult to obtain simultaneously for these types of manufactured barriers.

Another disadvantage of the manufacture of barrier by using dispersion coating is that the stability of the dispersion must be good to ensure good runnability. In order to obtain good stability of a dispersion, it is necessary to add stabilizing components.

However, by incorporating multiple components, it becomes more difficult to prepare the dispersion.

Another characteristic of the dispersion barrier is that a significant amount of water is added to the substrate during the formation of the barrier. This water must be evaporated away and a large amount of energy is therefore required for drying to ensure a dry barrier and complete film formation of the barrier layer. The temperature of the dry coating must normally be substantially above the glass transition temperature of the polymer to ensure that film formation proceeds. However, the use of high drying temperatures can also cause problems with blisters or adhesion between the barrier layer and the base substrate.

Another problem with high drying temperatures is that the tackiness of the polymer film increases due to the fact that the temperature will often be above the glass transition temperature.

Another problem with traditional dispersion barrier coating is that the viscosity is relatively low (and also the dry content) which creates a high level of penetration into the base substrate. This means not only that a larger amount of coating is required to ensure a coating without holes and with good barrier properties, but also that high energy for drying is required. For uncoated board, 15-25 g / m2 of dry coating is typically required to obtain a surface of the barrier layer without holes. Thus, there is a need for an improved method of making paper or board with one or more barrier layers in a cost effective manner.

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface of a fiber-based substrate with a barrier layer in an improved manner.

Another object of the present invention is to provide a method of adding a thin barrier layer to a surface of a fiber-based substrate.

A further object of the present invention is a fiber-based substrate with improved barrier properties.

The above-mentioned objects, as well as other advantages, are obtained by the method and the substrate according to the invention.

The invention relates to a method for providing a surface of a fiber-based substrate with a barrier layer, the barrier layer being formed by applying nanofibers to the surface by using electrospinning or melt spinning.

The barrier layer may be in the form of a film on the surface of the fiber-based substrate.

The film is formed upon finishing of the substrate after the application of the nanofibers to the surface. It is preferred that the finishing be done by raising the temperature of the applied nanofibers so that a film is formed. It is preferred that the temperature be raised above the glass transition temperature or melting temperature of the applied nanofibers to form a film.

It is possible for at least two components to be spun and applied simultaneously to the surface of the substrate. The simultaneous spinning of different components can take place through different nozzles or other feeding devices, so that one component is spun through one nozzle and another component through another. In this way, the barrier layer will contain a mixture of different nanofibers, which makes it possible to provide a barrier layer with different properties, ie makes it a composite material. ie at least two layers. It is thus possible to provide the different layers with different properties.

The barrier layer may contain more than one layer. It is preferred that the barrier layer has a dry content of 0.1-20 g / m 2, preferably 0.1-5 g / m 2 or more preferably 0.2-3 g / m 2. without holes on a porous surface with a small amount of applied nanofibers.

It is possible to form a continuous film. The fiber-based substrate can be provided with a coating layer to which the nanofibers are applied. In this way a smoother surface is obtained, which makes it possible to further reduce the amount of applied fibers.

The barrier layer of the substrate can be provided with a coating layer. It is preferred that the coating layer contains a polymer which is laminated or extrusion coated on the barrier layer.

The nanofibers are formed by electrospinning or melt spinning a polymer such as polyvinyl alcohol, lacquer, polystyrene, polybutadiene, polyurethanes, polyethylene dispersions, polypropylene, PLA, chitosan, starch, sodium carboxymethylcellulose, copolymers of polyethylene acrylate polyethylene dispersions, polyethylene terephthalate dispersions, mixtures or their modified equivalents to any of the mentioned components.

The electrospinning can be done with a liquid or a dispersion containing at least one polymer. It is also possible to use polymer in solid form or a wax as a starting material which is melted, ie melt spinning.

The barrier layer can also be provided with functional properties by adding a functional additive to the barrier. The functional additive can be spun together with the polymer. It is also possible that the functional additive is spun separately to form a separate layer of the barrier layers.

The invention also relates to a fiber-based substrate which contains a fiber-base layer and a barrier layer, the barrier layer being formed by electrospun or melt-spun nanofibers on the surface of the fiber-base layer.

The barrier layer is preferably a film formed by the applied nanofibers.

The film can be formed by molten nanofibers, i.e. the applied nanofibers can be melted to form said film. The film can also be formed by raising the temperature of the nanofibers to or above the glass transition temperature, whereby the fibers "flow" and a film is formed. It is possible that the film is continuous, i.e. it completely covers the surface of the fibrous substrate without holes etc which makes it possible for components to reach the surface of the fibrous substrate.

In some applications, it is not necessary to completely cover the entire surface of that fiber base surface to obtain adequate protection.

The film can also be discontinuous. 10 15 20 25 30 35 534 B75 The barrier can be a barrier against liquid, steam, oil, aroma, fat, lubricant, oil, solvent, heat, UV light and / or gas.

If the film is discontinuous, the barrier may be a barrier to oil, lubricant and / or grease. It has been found that the necessary barrier properties against oil, lubricant and / or grease can be obtained even if the film forming the barrier is discontinuous, i.e. it contains nanoholes or similar irregularities. This is because the contact angle between the film and the oil, the lubricant and / or the grease is large enough that the oil will not penetrate the barrier layer. This can be used for barrier properties for a short time, eg temporary grease / lubricant barrier.

The barrier layer may contain nanofibers of at least two components. By simultaneous spinning of different components, preferably through different nozzles or other feeding devices, it is possible to manufacture a barrier layer which contains at least two components. In this way the barrier layer can have different properties as one component can give barrier properties to a substance, such as water, and another component can give barrier properties to another substance. In this way it is possible to spin a component which will melt to e.g. lubricant. form a film and another component that will support the molten component and prevent it from penetrating too deeply into the base material, i.e. retaining them on the surface of the fiber-based substrate. It is thus possible that a single barrier layer provides protection against several different substances.

The barrier layer may contain at least two layers. It is possible that the barrier layer contains two or more layers. Each layer can have different properties, for example one layer can provide the substrate with barrier properties against steam and a second layer can provide the barrier with heat sealing properties. 10 15 20 25 30 35 534 8 The fiber base layer can be coated with any conventional coating before the application of nanofibers to the surface. The barrier layers are thus formed on the coated surface of the fiber-based layer. In this way, the barrier layer is formed on a smooth surface, which makes it possible to further reduce the amount of nanofibers applied.

The barrier layers of the fiber-based substrate can also be coated.

The invention also relates to a fiber-based substrate manufactured according to the method described above.

The present invention relates to a method of providing a surface of a fiber-based substrate with a barrier layer, the barrier layer being formed by applying nanofibers to the surface using electrospinning or melt spinning.

It has been found that application of nanofibers to a surface of a fiber-based substrate by using electrospinning or melt spinning it is possible to form a thin layer of nanofibers which will form a barrier layer on the surface. It has surprisingly been found that a thin layer of applied nanofibers is sufficient to completely cover an uneven surface, such as a surface of a fiber-based substrate. In addition, due to the characteristic fiber dimension and the fiber properties of the nanofibers made and applied by electrospinning or melt spinning, the penetration of the nanofibers into the substrate is negligible. The nanofibers will thus be applied to the surface and remain on the surface of the substrate. They will still bind to the surface satisfactorily due to chemical and / or physico-chemical interactions between the fibers of the substrate and the applied nanofibers. They may also have an internal extension which may form mechanical or physical interconnection of the fibers. The applied nanofibers will either join or melt on the surface of the substrate and form a film that will act as a barrier. Applying fibers to the surface before a complete film has formed requires a considerably smaller amount of coating, due to the fact that the penetration into the substrate is much lower or even insignificant compared to other barriers formed by other coating techniques on a fiber-based substrate. The formation of the film according to the invention consequently takes place through a network of fibers which can be compared with previous solutions where films are formed from a solution or a dispersion.

The amount of fibers added to the surface of the fiber-based substrate depends on various parameters, for example on the unevenness of the surface. It is preferred that the barrier layers have a weight (dry) of 0.1-20 g / m 2, preferably 0.1-5 g / m 2 and more preferably 0.2-3 g / m 2. If the surface to which the barrier layer is added is uneven, a larger amount of fibers must be added and it is preferred that the weight (dry) of the barrier layer is between 2-20 g / m2.

By optimizing the spinning ratio, it is possible to increase the spinning moisture so that the applied fibers fuse together into a film. The fibers that are first applied will be dry or have a high dry content, which means that the fibers have a high rheology. This is partly because the surface to which they are applied is dry. The spinning conditions will then change so that the following applied fibers are wetter, ie semi-dry. This results in the fibers fusing together into a film which acts as an excellent barrier. The dryness and / or firmness of the liquid or air used in electrospinning or melt spinning can be controlled so that the fibers fuse together into a film. It is also possible to control the humidity, temperature, production speed and distance during spinning so that the fibers form a film. In this way, it is possible to manufacture a fiber-based substrate in a very simple manner.

After the nanofibers have been applied to the surface, the substrate or surface of the substrate is post-treated to form the nanofibers. It is preferred to use heat treatment which will raise the temperature of the applied nanofibers so that the properties of the applied nanofibers are changed to form a film. to raise the temperature to or above the glass transition temperature or the melting temperature of the nanofibers. In this way, the properties of the applied nanofibers change, for example they begin to "float" or melt. It is preferred and they will then form a film which will act as a barrier layer on the fiber-based substrate.

Depending on the material used for the manufacture of the nanofibers and the time of treatment, it may not be necessary to raise the temperature to or above the glass transition temperature. For some materials, it may be sufficient to raise the temperature slightly, still below the glass transition temperature, for the properties of the applied nanofibers to change and form a film. infrared air dryer, plasma, steam, laser UV, EB or any other known technology. It is also possible to use hot fusing or hot rolling in which the applied fibers are heated and at the same time formed into a thin film on the substrate.

The heating can be done by using flame, dryers, solder roll, The substance or substances to be formed into nanofibers by using electrospinning or melt spinning can be polymers or a mixture of polymers. Suitable polymers can be selected from, for example, polyolefins, polyvinyls, polyamides, polyimides, polyacrylates, polyesters and mixtures thereof. It is especially preferred to use polyvinyl alcohol, lacquer, polystyrene, polybutadiene, polyurethanes, polyethylene PLA, chitosan, dispersions, polypropylene, starch, sodium carboxymethylcellulose, copolymers of acrylate, polyvinyl acetate, polyethylene ethylene polyethylene ethylene polyethylene dispersions, mixtures or their modified equivalents to any of the components mentioned. The polymer used depends on the end use of the fiber-based substrate. The different polymers form a barrier layer against different properties, for example PVA will form a barrier layer against lubricants.

The present invention makes it possible to provide a barrier layer containing at least two components. This can be done by spinning two or more components simultaneously which are then applied to the surface of the substrate. The simultaneous spinning of two or more components can take place through different nozzles or other feeding devices so that one component is spun through one nozzle and another component through another. In this way, the barrier layer will contain a mixture of different nanofibers, which makes it possible to provide an individual barrier layer with different properties, ie to manufacture a composite material. For example, one component may impart barrier properties to a substance such as water and another component may impart barrier properties to another substance such as lubricant. In this way, it is also possible to spin a component that will melt and form a film and another component that will support the molten component and prevent it from penetrating too deep into the base material, i.e. retaining them on the surface of the fiber-based substrate. . It is thus possible that a single barrier layer contains protection against several different substances.

A major advantage of the present invention is that it is possible to provide the barrier layer with more than one layer in a simple manner. It is thus possible to manufacture a barrier layer which meets different properties which have previously required different process steps. In this way it is possible to provide the barrier layer with several layers with different properties, for example a primary layer, a barrier layer, a protective layer, a heat sealing layer and / or a blocking layer.

The use of different polymer dispersions gives different properties. For example, a polyurethane dispersion will provide a barrier against aromas, greases and lubricants as well as sealing properties. Thus, a fiber-based substrate having a polyurethane barrier will be easy to seal to form a package while having excellent barrier properties. If the polyurethane barrier layers are combined with an ethylene layer, the fiber-based substrate will also have a barrier to water.

The surface of the fiber-based substrate can be provided with a coating layer. The nanofibers will thus be applied to the coating layer of the fiber-based substrate. In this way, the application of the coating layer takes place on a smooth surface and the amount of nanofibers can be further reduced.

The coating can be any conventional coating batter, such as calcium carbonate or kaolin.

The barrier layer of the substrate can be provided with a coating layer. It is preferred that the coating layer contains a polymer which is laminated or extrusion coated on the barrier layer. In this way, the barrier layer may contain a primer that can increase the adhesion between the fiber-based substrate and an extrusion-coated layer, which makes it possible to increase the speed of the extrusion coating process. The coating layer may also contain any conventional coating component, both polymeric layers as well as pigment coating layers.

It is also possible to provide the barrier layer with functional properties by adding a functional additive to the spun medium. Possible additives can be fillers which can increase the whiteness or provide the substrate with UV protection or absorbents which can capture taste and The functional additive can be mixed with the medium, preferably odor chemicals and thus reduce the problems. a polymer dispersion, and thus spun together with the polymer. The nanofibers formed thus contain a mixture of polymer nanofibers and nanofibers of the additive.

It is also possible to incorporate an additive into the formed nanofibers. Another possibility is to spin the functional additive simultaneously with a polymer, described above. as It is also possible to use a solid medium such as a solid polymer or a wax as a starting material for the process of forming nanofibers. This is normally called melt spinning. A major advantage of this method is that no water or liquid is added to the surface of the substrate and thus there is no need to evaporate the added water by increased drying. It is thus possible to reduce drying, which saves both energy and time.

The fiber-based substrate is preferably a paper or board made of lignocellulose. Other fiber-based substrates such as non-woven or textiles can also be used.

The formation of the particles takes place by electrospinning or melt spinning, whereby ultrafine fibers are formed. The diameter of a single fiber can, for example, be less than 5 μm or even less than 40 nm. The term electrospinning or melt spinning relates to the generation of nanosized fibers due to viscoelastic and electrostatic forces. The medium from which the fibers are formed may be a foam, a melt or a solid material, preferably a polymer.

It is preferred that the formed nanofibers be applied to a paper or board substrate. The particles can, for example, be applied to a moving web of paper or cardboard in the papermaking process. The method according to the invention can thus be used for, for example, coating or gluing paper or cardboard. The method can be used to incorporate various types of polymer fibers directly onto or incorporated into the surface of the paper or board.

The electrostatic formation of the particle according to the present invention can take place by means of a conventional apparatus suitable for electrospinning. The apparatus may include a collector, a supply section and a voltage source adapted to provide an electrical voltage difference between the collector and the supply section. The collector may be a metal plate to support the substrate, although a plate, roller, belt, cylinder or the like may also be possible to use. The electrostatic voltage is preferably between 40 and 60 kV, and the distance between the medium and the substrate is preferably between 10 and 300 mm, more preferably around 50 mm.

Electrospinning of the particles can take place by using both direct and / or alternating voltage. In one embodiment of the invention, the electrostatic treatment takes place in the presence of alternating current (AC) to apply an alternating voltage to one of the electrodes forming the electric field, applied either to the supply section or to the electric field. This can be obtained by, for example, an alternating voltage can the collector. The use of AC potentials gives rise to an improved coverage of the applied surface of the formed particles.

The electrospinning can also take place by simultaneously in this way the shape of the particles formed in the process can be varied. According to use both alternating current and direct current. In one embodiment, an alternating voltage is applied to the collector and a direct voltage to the supply section, whereby particles with a form of rather large fibers can be manufactured. In another embodiment, an alternating voltage is applied to the supply section and a direct voltage is applied to the collector, whereby fine particles can be manufactured. 53 15 B75 14 The feed section of the suitable apparatus may be, for example, an opening, one or a number of nozzles or it is also possible to spin from an open surface, i.e. a free-flowing liquid surface or a roller.

The invention is further described with reference to some examples below. The invention is not limited to the particular process steps and materials disclosed herein.

The results are shown in the accompanying figures. Brief description of the figures: Figure 1 a) shows an uncoated board used as a reference.

Figure 1 b) shows an e-spun board coated with 0.3 g / m2.

Figure 1 c) shows an e-spun cardboard coated with 1.2 9 / m2.

Figure 2 a) shows an e-spun carton with a coating weight (dry) of 1.2 g / m2 and heated in the oven at 550 ° C for 1 s.

Figure 2 b) shows an e-spun carton with a coating weight (dry) of 1.2 g / m2 and heated in the oven at 550 ° C for 3 s.

Figure 3 a) shows a carton with an electrospinning coating of Cartaseal VGL after finishing.

Figure 3 b) shows a carton with an electrospinning coating of Cartaseal RTD after finishing.

Example 1 Nanofibers made using electrospinning were applied to an uncoated board sample.

The polymer used was polyvinyl alcohol and the concentration of the e-spun liquid was slightly less than 10% by weight, while the applied fibers have a high dry content due to the evaporation that occurs during the movement between the nozzle and the substrate.

The attached images were taken with a scanning electron microscope (SEM) and Figure 1a shows an image of an uncoated cardboard used as a reference. The fibers and pores between the fibers are clearly seen in this image. In Figures 1b and 1c, the weight of the applied nanofibers is gradually increased, which can be seen as a larger amount of nanofibers but also that a local fiber-fiber fusion starts.

The smooth spots shown in Figure 1c indicate that a film has formed. These stains were obtained by changing the conditions of the electrospinning so that the applied nanofibers were partially wet, fused together into a film. i.e. semi-dry, and thus No external heat was thus used in this case to obtain the formation of the film.

Example 2 Two carton samples coated with e-spun nanofibers to a weight (dry) of 1.2 g / m 2 described in Example 1 were heat treated.

By heat treating the applied e-spun fibers, it is possible to melt the applied fibers to form a film.

The weight of the coating in this case was quite small but it still covered almost the entire carton which shows the advantages of the present invention.

The carton samples were treated in an oven at 550 ° C for 1s and 3s, respectively. Figures 2a and 2b show the effect of finishing the spun-coated samples.

Example 3 Commercial barrier chemical (Cartaseal, Clariant) was tested and applied to cardboard by said application. In this case, the flow properties were adjusted with polyethylene oxide. or coating method described above.

The recipe was: - 2000 g Cartaseal VGL and RTD respectively of 10% dry matter - 200 g polyethylene oxide 600,000 of 6% 534 E? B 16 E-spun fibers were thus formed on the substrate. In this specific case, an uneven substrate was used and the goal was to have a coating weight (dry) of 10 g / m 2. The carton was then dried at 115 ° C for 10 minutes and SBM images were taken on the spun coated carton.

The result is shown in Figure 3a and Figure 3b which shows that full coverage was obtained and that there are no holes.

Table I shows the results of the grease / lubricant resistance tests according to a modified ASTM F119-82 standard test procedure that includes tests for specific chemicals at a given temperature (40 ° C).

Table I Chemical Resistance to lubricant by Resistance to lubricant by carton, carton to TLC Time for plate, Time for transparency penetration Cartaseal VGL> 52 h> 52 h Cartaseal RTD> 52 h> 52 h

Claims (27)

18 Patent claims

1. l. A method for providing a surface of a fiberbased substrate with a barrier layer wherein the barrierlayer is formed by depositing nanofibers on the surface by the use of electrospinning or meltspinning.

2. The method according to claim l, whereinthe barrier layer is formed as a film on the surface of the fiber based substrate.

3. The method according to claim 2, whereinthe film is formed by post treating the substrate after the depositing of nanofibers on the surface.

4. The method according to claim 3, whereinsaid post treatment is done by increasing thetemperature so that the deposited nanofibers form a film.

5. The method according to claim 4 wherein thetemperature is increased to or above the glasstransition temperature or melting temperature of the deposited nanofibers so that a film is formed.

6. The method according to any of thepreceding claims wherein more at least two componentsare spun simultaneously in order to deposit nanofibersof the components to the surface of the substrate in a single step.

7. The method according to any of thepreceding claims wherein the barrier layer comprises at least two layers. 19

8. The method according to any one of thepreceding claims, wherein the barrier layer has a dryweight of O.l-20 g/m2, preferably between O.l-5 g/m2 or even more preferably 0.2-3 g/m2.

9. The method according to any of thepreceding claims, wherein the surface of the fiber basedsubstrate is provided with a coating layer before the nanofibers are deposited on the surface.

10. The method according to any of thepreceding claims, wherein the barrier layer is provided with a coating layer.

11. ll. The method according to any of thepreceding claims wherein the nanofibers are formed byelectrospinning or meltspinning a polymer, such aspolyvinyl alcohol, varnish, polystyrene, polybutadiene,polyurethanes, polyethylene dispersions, polypropylene,PLA, chitosan, starch, sodium carboxymethyl cellulose,acrylate copolymers,polyvinyl acetate, poly ethyleneoxide, polyethylene dispersions, polyethyleneterephthalate dispersions, mixtures or its modified analogues of any of the mentioned components.

12. l2. The method according to claim ll whereinthe electrospinning is done with a liquid or dispersion comprising the polymer.

13. l3. The method according to any of thepreceding claims wherein the barrier layer further isprovided with a functional property by addition of a functional additive.

14. The method according to claim 13 whereinthe functional additive is spun together with the polymer.

15. The method according to claim 13 whereinthe functional additive is spun as a separate layer of the barrier layers.

16. A fiber based substrate which comprises afiber base layer and a barrier layer wherein the barrierlayer is formed by electrospun or meltspun nanofiberswhich are deposited on the surface of the fiber base layer.

17. The fiber based substrate according to claim 16 wherein the barrier layer is a film.

18. The fiber bases substrate according toclaim 17 wherein the deposited nanofibers are melted to form said film.

19. The fiber based substrate according to any of claims 17-18 wherein the film is continuous.

20. The fiber based substrate according to any of claims 17-18, wherein the film is discontinuous.

21. The fiber based substrate according to anyof claims 16-20 wherein the barrier is a barrier againstliquid, vapour, oil, solvents, heat, uv-light, aroma and/or gas.

22. 21 The fiber based substrate according to claim 20 wherein the barrier is a barrier against oil, grease and/or fat.

23. of claims The fiber based substrate according to l6-22 wherein the barrier layer comprises least two components.

24.of claims least two

25. The fiber based substrate according tol6-23 wherein the barrier layer comprises layers. The fiber based substrate according to of the claims 16-24 wherein the fiber base layer is coated and the barrier layer is formed on the coated surface of the fiber base layer.

26. of the claims l6-25 wherein the barrier layer is coated.

27. anyat anyat any The fiber based substrate according to any A fiber based substrate produced according to the method according to claims l-15.